In recent years, along with the miniaturization of semiconductor devices and the demand for higher performance, a high permittivity film (high-K film) has been used as a gate insulating film. Hafnium oxide-based materials have drawn recent attention as being used as a gate insulating film. Attempts have been made to enhance the (relative) permittivity of material such as a hafnium oxide (HfO2) and to reduce an equivalent oxide thickness (EOT).
As a method of increasing the relative permittivity of HfO2, there is proposed, e.g., a method of thermally treating an HfO2 film at a high temperature. However, the above proposed method suffers from a problem in that the HfO2 is crystallized by the high temperature heat treatment and that a leak current is increased due to an electric conduction through a grain boundary thus generated.
Taking a semiconductor device manufacturing process into account, due to the heat load constraints in different processes, it is desirable that an insulating film having a high relative permittivity can be provided through the heat treatments performed over a wide temperature range.
In a transistor manufacturing process, e.g., a so-called gate last process in which a source/drain forming step and a channel forming step precede a gate insulating film forming step, heat load constraints are imposed on the source, the drain and the channel thus formed. This poses a problem in that the gate insulating film cannot be subjected to a heat treatment at a high temperature.